In C₄ Plants, Photosynthesis Operates More Quickly and with Less

question 91

Multiple Choice

In C₄ plants, photosynthesis operates more quickly and with less need for widely open stomata than in C₃ plants. What characteristics of the enzyme PEP carboxylase are responsible for these differences?

• A)PEP carboxylase is located in the cytoplasm, so it is in closer contact with its substrate than rubisco, which is located in the chloroplast.
• B)PEP carboxylase has a higher catalytic rate than rubisco, which results in an increase in CO₂ concentrations in bundle-sheath cells.
• C)PEP carboxylase is a much smaller enzyme than rubisco and, therefore, is present at much higher concentrations in C₄ plant cells.
• D)PEP carboxylase is not consumed in its reaction with HCO₃^-.

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